dont use chatgpt, it isnt a great revision tool. learn the information, and if you don't understand it try and check multiple revision guides/notes to see it worded differently, if that helps. Try and rephrase them in your own words to see how much you do understand. look at past paper questions to see what comes up most and prioritise those and your weakest areas. see what kind of understanding you need. look at mark schemes to know what they expect from you. i'd also recommend the app knowunity, you can use it for free and you can find revision notes, flashcards, etc made by other students, and you can ask questions in subject group chats about topics or questions you are struggling with (sometimes it can take a few days to get a response, the app is kinda dead, but you will usually get one). and finally, good luck, and don't stress. these are only mocks, they are there so that you and your teachers know what you need to do to improve, so that you can perform to the best of your ability in the summer